It's something that's arbitrarily introduced without prior justification. It's when the writer can't think of a way out of the problem and just makes up some random thing out of the blue that conveniently fixes everything without the heroes having to do anything.

^^That's^^ my definition of a plot device and plot device is part of the GOOGLE definition for Dues Ex Machina. So I am therefore sticking to my original post.

__________________Doctor Who Episode "FLATLINE".

THE DOCTOR: I mean this is embarrassing.I'm from the race that built the T.A.R.D.I.S.Dimensions are kind of our thing. So why can't I understand this?